In general, work machines, such as a hydraulic excavator, are equipped with various fluid pressure actuators such as hydraulic cylinders. When the fluid pressure actuators are, for example, hydraulic cylinders for actuating a front work linkage mounted on a hydraulic excavator, returning an operating lever for the hydraulic cylinders abruptly from an operating position to a neutral position interrupts oil supply or discharge for the hydraulic cylinders. This causes kinetic energy remaining in the hydraulic cylinders to generate a pressure vibration whose natural frequency is determined by the compression of the oil in oil chambers of the hydraulic cylinder or in supply or discharge channels and the inertia of a weight load acting on the hydraulic cylinders. The pressure vibration lasts for a long time until the remaining kinetic energy disappears in the form of heat loss, giving an operator an unpleasant feeling and impairing operating efficiency.
There is thus a need for a technique for quickly dampening such pressure vibrations generated in fluid pressure actuators upon returning an operating lever from an operating position to a neutral position.
The control valve disclosed in Japanese Published Unexamined Patent Application No. 13-280305, which is controlled to dampen the pressure vibration, is arranged so that the supply and discharge control for a rod side oil chamber and a head side oil chamber of a hydraulic cylinder is carried out by a single spool valve. As a result, for example, when a pressure vibration is detected in the fluid channel for operating the actuators connected to the head side oil chamber and the control valve is displaced in a direction for damping the pressure vibration, the displacement of the valve can allow oil to be supplied to and discharged from not only the head side oil chamber, but also the rod side oil chamber. When this occurs the frequency of the generated pressure vibration is not only the same at both the rod and head sides of the hydraulic cylinder, but the phase is reversed between the two sides. Hence, the displacement of the control valve for damping the pressure vibration at the head side may not be effective in damping a pressure vibration also caused at the rod side.
In addition, a front work linkage mounted on a hydraulic excavator includes a plurality of members that are coupled together in a mutually swingable manner, such as a boom whose base end is pivoted on the machine body to allow the boom to move vertically, a stick pivoted on the front end of the boom to be swingable back and forth, and the like, and hydraulic cylinders for swinging these members. When a hydraulic cylinder for one member is brought to a sudden stop in such a machine, a shock caused by the stoppage is transmitted to the hydraulic circuit of a hydraulic cylinder for another member, generating a pressure vibration in the hydraulic cylinder for another member. This results in a vibration of the entire front work linkage.
This disclosure is aimed at providing solutions to these and other problems commonly known to those skilled in the art.